1. Field of the Invention
The invention relates to a method for extracting silica from herbaceous plants, and more particularly a method for extracting silica from herbaceous plants, which is capable of extracting high purity amorphous silica from seed shell of various herbaceous plants.
2. Description of the Related Art
Silica is a compound of oxygen and silicon, commonly called silicon dioxide, which is one of the most abundant materials in the lithosphere. It is said that it exists in the lithosphere in great quantities, as much as comprising about 59% by weight of lithosphere.
The silica has been used in preparing various materials for building construction or durable materials including compressed glass, etc. In recent, as high purity silica powder is available, it is also possible to be applied as an additive in cosmetics, medications, semiconductors, films, waxes and fineceramics. Researches and studies are being conducted to seek a more improved method for producing high purity silica powder.
One conventional method commonly used to produce silica includes finely grinding an ore. The resulting powder is added to Na2CO3 and heated to a high temperature to form sodium silicates in different crystal forms, such as Na2SiO4, Na4SiO4 and Na2Si2O5, etc. The sodium silicates are well soluble in water. An acid is added to the aqueous solution of such sodium silicates and heated, resulting in crystalline silica.
However, the silica obtained from minerals has a high hardness and contains a large amount of impurities. Therefore, it has a limitation in application as an additive for those which require high purity, such as medications, semiconductors and the like. Further, the conventional method has a defect that the quantity of produced silica is limited.
In recent, there are conducted researches and studies in a part to seek a method for extracting silica from various herbaceous plants.
In particular, it has been attempted to produce silica using rice hulls. The obtained silica has purity comparable to the silica from minerals, however it has high contents of crystals and high hardness. Thus, its application is limited.